The Senate voted Tuesday to begin debating a replacement for the Affordable Care Act. It remains uncertain as to what that replacement might look like. No formal legislation has been drafted. But senators moved to take the procedural first step, known as a "motion to proceed." The vote was 51-50, with Vice President Pence casting the tiebreaking vote.

Debate will now begin, most likely on a measure to fully repeal the law, also known as Obamacare.

Updated July 25, 5:25 PM ET: Tuesday afternoon, the Senate voted to send the original House legislation repealing and replacing the Affordable Care Act to the floor. (Details below on the proposals/bills.)

But the Senate is only using it as a vehicle to add amendments that will change it substantially. The first amendment would phase out many of the Affordable Care Act's provisions over two years.